1. Field of the Invention
The present invention relates to a display device with a touch panel.
2. Description of the Related Art
In recent years, in information communication terminals such as computers, display devices with a touch panel input function that are configured by placing a touch panel on a display device have been widely used. Among them, a liquid crystal display device is generally in widespread use as a device to provide a display function. The liquid crystal display device is a device that changes, using a change in electric field, the alignment of a liquid crystal composition contained between two substrates of a thin film transistor substrate (hereinafter referred to as TFT (Thin Film Transistor) substrate) and a color filter substrate and controls the degree of light transmission to thereby display an image. In such a liquid crystal display device, an IPS (In Plane Switching) system has been widely used in which a so-called lateral electric field is formed by arranging both of pixel electrodes and common electrodes on the TFT substrate side to realize wide-viewing angle display.
A touch panel is an input device that recognizes coordinates on a panel touched using a user s finger or the like and causes a processing device to perform processing based on the coordinates. In the touch panel, a resistive film system that detects a change in the resistance value of a touched portion, an optical sensor system that detects a change in the light intensity of a portion blocked by a touch, an electrostatic capacitive coupling system that detects a change in capacitance, and the like have been known. The electrostatic capacitive coupling system has been widely used because, for example, it has high panel transmittance and thus does not reduce display image quality and it has high durability with no contact with other electrodes.
In recent years, due to the demand for reductions in the size and thickness of information communication terminals, a further reduction in the thickness of the liquid crystal display device with a touch panel has been required. JP 2009-244958 A discloses, in liquid crystal display devices of the IPS system, a liquid crystal display device with a touch panel whose further reduction in thickness is achieved by using common electrodes of the liquid crystal display device as drive electrodes of the touch panel.
For extracting a signal from a wiring on a glass substrate of a TFT substrate, a flexible cable such as an FPC (Flexible Printed Circuit) is generally connected using a conductive adhesive material such as an ACF (Anisotropic Conductive Film). In this case, a portion of the TFT substrate at which the FPC is connected is transparent and thus visible from the opposite side of the TFT substrate surface on which the FPC is connected. Therefore, by previously preparing an alignment mark on the TFT substrate at the stage of a thin film formation step, the FPC can be connected with high accuracy while viewing the alignment mark.
On the other hand, in the liquid crystal display device with a touch panel disclosed in JP 2009-244958 A, since a detection electrode for touch detection is arranged on a color filter substrate, a signal has to be extracted from over the color filter substrate. However, since alight shielding film is formed at the peripheral portion of the color filter substrate and the portion is not transparent, alignment using an alignment mark in the same manner as in the TFT substrate is difficult.